The Great Basin is a large, arid region of the western United States, commonly defined as the contiguous watershed region, roughly between the Rocky Mountains and the Sierra Nevada, that has no natural outlet to the sea. The Great Basin Desert is defined by the extent of characteristic plant species, and covers a somewhat different area. The Great Basin Culture Area, home to the Great Basin tribes also extends further to the north and east than the hydrographic basin.

The 200,000 square mile (500,000 square km) intermontane plateau covers most of Nevada and over half of Utah, as well as parts of California, Idaho, Oregon and Wyoming. The Great Basin is not a single basin, but rather a series of contiguous watersheds, bounded on the west by watersheds of the Sacramento-San Joaquin and Klamath rivers, on the north by the watershed of the Columbia-Snake, and on the south and east by the watershed of the Colorado-Green.

Much of the Great Basin, especially across northern Nevada, consists of a series of isolated mountain ranges and intervening valleys, a geographical configuration known as the Basin and Range Province. Additionally the Great Basin contains two large expansive playas that are the lakebed remnants of prehistoric lakes that existed in the basin during the last ice age but have since largely dried up. Lake Bonneville, the prehistoric ancestor of the Great Salt Lake, covered much of Utah, leaving behind the Bonneville Salt Flats. Likewise Lake Lahontan extended across much of northwestern Nevada and neighboring states, leaving behind such remnants as the Black Rock Desert, Carson Sink, Humboldt Sink, Walker Lake, Pyramid Lake, Winnemucca Lake, and Honey Lake, each of which now forms a separate watershed within the basin.

The Basin and Range province's dynamic fault history has profoundly affected the region's water drainage system. Most precipitation in the Great Basin falls in the form of snow that melts in the spring. Rain that reaches the ground, or snow that melts, quickly evaporates in the dry desert environment. Some of the water that does not evaporate sinks into the ground to become ground water. The remaining water flows into streams and collects in short-lived lakes called playas on the valley floor and eventually evaporates. Any water that falls as rain or snow into this region does not escape out of it; not one of the streams that originate within this basin ever find an outlet to the ocean. The extent of internal drainage, the area in which surface water cannot reach the ocean, defines the geographic region called the Great Basin.

The Great Basin's internal drainage results from blockage of water movement by high fault-created mountains and by lack of sufficient water flow to merge with larger drainages outside of the Great Basin. Much of the present-day Great Basin would drain to the sea - just as it did in the recent Ice Ages - if there were more rain and snowfall.

Geology

The Great Basin is considered by geologists to be in the process of stretching and cracking. Although elevated, the crust here is actually relatively thin, and getting thinner. Some geologists speculate that the Pacific Rise rift zone may be destined in the distant future to split the Great Basin, possibly by way of the Imperial Valley and Death Valley, letting the sea in from the Gulf of California.

Flora and Fauna

The Great Basin is predominantly high altitude desert, with the lowest basins just below 4,000 feet and several peaks over 12,000 feet. Most areas are dominated by shrubs, mostly of the Atriplex genus at the lowest elevations and sagebrush at higher elevations. Open woodlands consisting of Utah Juniper, Single-leaf Pinyon (mostly southern areas) or Curl-leaf Mountain Mahogany (mostly northern areas) form on the slopes of most ranges. Stands of Limber Pine and Great Basin Bristlecone Pine can be found in some of the higher ranges. Cottonwoods and Quaking Aspen groves exist in areas with dependable water.

Lagomorphs such as Black-tailed Jackrabbit and Desert Cottontail and the coyotes that prey on them are the mammals most often encountered by humans. Ground squirrels are common, but they generally venture above ground in only the spring and early summer. Packrats, Kangaroo rats and other small rodents are also common, but these are predominantly nocturnal. Pronghorn, Mule Deer, Wapiti, Bighorn Sheep and Mountain Lion are present but uncommon.

Small lizards such as the Western Fence lizard, Leopard lizard and Horny toad are common, especially in lower elevations. Rattlesnakes and Gopher snakes are also present.

Shorebirds such as Phalaropes and Curlews can be found in wet areas. American White Pelicans are common at Pyramid Lake. Golden Eagles are perhaps more common in the Great Basin than anywhere else in the US. Mourning Dove, Western Meadowlark, Black-billed Magpie and Common Raven are other common bird species.

Large invertebrates include tarantulas (Aphonopelma genus) and Mormon crickets.

Chukar, Grey Partridge and Himalayan Snowcock have been successfully introduced to the Great Basin, although the latter has only thrived in the Ruby Mountains. Cheatgrass, which was unintentionally introduced, forms a critical portion of their diets. Feral horses (Mustangs) are another highly successful, though controversial, alien species. Most of the Great Basin is open range and domestic cattle and sheep are widespread.

History

The history of human habitation in the Great Basin goes back at least 12,000 years. Archaeological evidence of primitive habitation sites along the shore of prehistoric Lake Lahontan date from the end of the ice age when its shoreline was approximately 500 ft (150 m) higher along the sides of the surrounding mountains.

At the time of the arrival of Europeans, the region was inhabited by a broad group of Uto-Aztecan-speaking Native American tribes known collectively as the Great Basin tribes, including the Shoshone, Ute, and Paiute. The first Europeans to encounter the area were the early Spanish explorers in the southwest in the late 18th century. By the early 19th century, fur trappers from the Hudson's Bay Company had explored the upper Basin in the Oregon Country. The first comprehensive and accurate map of the region was made by John C. Frémont during several expeditions across the region in the 1840s.

The United States acquired complete control of the area through the 1846 Oregon Treaty (giving it the portion north of the 42nd parallel) and the 1848 Treaty of Guadalupe Hidalgo. The first large-scale white settlement in the region was by early Mormon pioneers in the late 1840s in the arable areas around Salt Lake City and the Cache Valley. The Mormons quickly established a provisional government and drafted a proposal for a new state, called the State of Deseret, that encompass the entire Great Basin, as well as the coast of southern California. The region became successively organized by the creation of the Oregon Territory in 1848, the admission of California to the Union in 1850, and the creation of the Utah Territory in 1850. The discovery of gold in California in 1848 brought waves of emigrants across the Great Basin along the California Trail, which followed the Humboldt River across Nevada.

The part of the first North American transcontinental railroad that was build by the Central Pacific railroad crossed the Great Basic between Reno, Nevada, and Ogden, Utah. Another major railroad southwest from Salt Lake City into Nevada lead to the founding of Las Vegas, Nevada.

In 1986, the Great Basin National Park was established by the Federal Government, encompassing 122 square miles of land in Nevada, near the Utah border. The new National Park subsumed the much smaller Lehman Caves National Monument, which had been established in 1922. All of this land is within the Great Basin, and it includes basin and mountainous land, and it is the home of much wildlife.

In the 1950's, the area northeast of Las Vegas was the site of numerous above-ground atomic bomb tests, followed in the 1960's by underground testing.

Present Habitation

The Basin has remained among the most sparsely-inhabited areas of the United States. The two largest cities in the basin are Salt Lake City, Utah on its eastern edge and Reno, Nevada on its western edge. Smaller cities in the basin include Carson City, Nevada; Winnemucca, Nevada; Elko, Nevada; Ogden, Utah; Provo, Utah; and Logan, Utah.

The Great Basin is traversed by major long-distance railroads and expressways, such as the parts of Interstate-80 between Reno and Salt Lake City, Interstate-15 between California and Idaho, and Interstate-70 between its junction with Interstate-15 in Utah and westmost Colorado.